Security 2025 chapter edits (#4357)

* Edit security.md for clarity and grammar improvements

Refine language and improve clarity in security.md up to section on "keywords for script-src"

* update quote text

* updates up to the malpractices on the web section

* add remaining updates for review

* Update src/content/en/2025/security.md

Co-authored-by: Barry Pollard <barrypollard@google.com>

* Update src/content/en/2025/security.md

Co-authored-by: Barry Pollard <barrypollard@google.com>

* Update src/content/en/2025/security.md

Co-authored-by: Barry Pollard <barrypollard@google.com>

* Update src/content/en/2025/security.md

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Co-authored-by: Barry Pollard <barrypollard@google.com>

Author: clarkio